Method and composition for inhibiting post-surgical adhesions

ABSTRACT

A method and compositions for reducing post-surgical adhesion formation/reformation in mammals following surgical injury to a body cavity or organs situated therein. The aqueous compositions comprising pentoxifylline and a polyoxyalkylene block copolymer are applied to the injured areas subsequent to surgical injury.

This is a continuation of application Ser. No. 08/540,229, filed Oct. 6, 1995, now U.S. Pat. No. 5,843,470.

BACKGROUND OF THE INVENTION

1. Field of the invention

This invention relates to methods and compositions for inhibiting post-surgical adhesions in the mammalian abdominal or thoracic cavity or other body spaces, whether accidentally or surgically created.

2. Description of the Prior Art

There is a need for improved methods and compositions for inhibiting adhesion formation/reformation in body spaces of mammals, whether accidentally or surgically created. According to Ellis in a review entitled, "The Cause And Prevention of Post-operative Intraperitoneal Adhesions," in Surgery, Gynecology and Obstetrics for September 1971, volume 133, pages 497-509, at pages 502-503, the prevention of adhesions has been the subject of an enormous amount of work since the beginning of this century. According to Ellis, these attempts have included means of preventing the fibrin-coated walls of the intestine from reaching each other by distending the abdomen with oxygen or filling the abdomen with saline solution, paraffin, olive oil, lanolin, concentrated dextrose solution, macromolecular solutions of all sorts, and silicones.

Menzies and Ellis in a review entitled, "Intestinal Obstruction from Adhesions--How Big is the Problem?" Annals of the Royal College of Surgeons of England, vol 72 pages 60-63, 1990 reported finding adhesions in 10.4% of 115 patients with first-time laparotomies while 93% of 210 patients had intra-abdominal adhesions due to previous surgery. Admission for intestinal obstruction was made for 0.9% of 28,297 general surgery patients while 3.3% of 4,502 laparotomy patients were admitted for intestinal obstruction due to adhesions. These data emphasize the magnitude of readhesions after adhesiolysis or from subsequent surgical procedures. The authors state on p. 62, that there is currently no effective treatment that prevents their recurrence.

High molecular weight dextran either alone or in combination with dextrose has been used to prevent peritoneal adhesions subsequent to surgery. Dextran is clinically standardized to a low molecular weight of about 75,000 by partial hydrolysis and factional precipitation of the high molecular weight particles which normally have molecular weights up to 200,000. Dextran is a polymer of glucose which has a chain-like structure and is produced from sucrose by Lenconostoc bacteria. In articles appearing in Fertility and Sterility, volume 33, number 6, June 1980, pages 660-662, Holtz, Baker, and Tsai and volume 34, number 4, October, 1980, pages 394-395, by Holtz and Baker, results are reported of the adhesion reducing effects of a 32% (aqueous) solution of Dextran 70 containing 10% dextrose (sold under the trade name HYSKON by Pharmacia, of Piscataway, N.J.). Holtz et al postulate several mechanisms of action in the prevention of peritoneal adhesions utilizing HYSKON® including a simple mechanical separation of adjacent surfaces, termed a hydroflotation effect.

Project coordinator diZerega and several contributors have reported the results of a large study in an article entitled, "Reduction of Post-operative Pelvic Adhesions with Intraperitoneal 32% Dextran 70: A Prospective, Randomized Clinical Trial," in Fertility and Sterility, volume 40, number 5, for November 1983, pages 612-619. The authors, on page 618, indicate that the use of Dextran intraperitoneally has limitations such as the reported tendency of HYSKON to support bacterial proliferation and concern over the anaphylactoid potential of dextran. In addition, the benefit of Dextran 70 in preventing post-operative adhesions was shown to be limited to the lower regions of the pelvis.

Borten, Seibert, and Taymor in Obsterics and Gynecology, vol 61, number Jun., 6, 1983, pages 755-757 report in an article entitled, "Recurrent Anaphylactic Reaction to Intraperitoneal Dextran 75 Used for Prevention of Postsugical Adhesions". These authors indicate that anaphylactic reaction to Dextran administered intravenously is well documented and report such a reaction after intraperitoneal administration of Dextran.

The use of ethylene oxide/propylene oxide block copolymers as surfactants in surgical scrub solutions and the topical application of 10% solutions of these copolymers to wounds is described in Edlich et al in the Journal of Surgical Research, volume 14, number 4, April 1973, pages 277-284. The test results indicate that copolymers having an ethylene oxide:propylene oxide ratio of 4:1 provide less inflammatory response in a wound to which the copolymer is applied in comparison with a copolymer having an ethylene oxide:propylene oxide ratio of 1:4. There is no indication by Edlich et al or any cited prior art that such copolymers are useful in reducing postoperative adhesions or that isotonic, aqueous solutions of such copolymers are useful in reducing post-operative adhesions.

Over the years, methods have been developed to achieve the efficient delivery of a therapeutic drug to a mammalian body part requiring pharmaceutical treatment. Use of an aqueous composition which can be applied at room temperature as a liquid but which forms a semi solid gel when warmed to body temperature has been utilized as a vehicle for drug delivery. Such a system combines ease of application with greater retention at the site requiring treatment than would be the case if the aqueous composition were not converted to a gel as it is warmed to mammalian body temperature. In U.S. Pat. No. 4,188,373, PLURONIC® polyols are used in aqueous compositions to provide thermally gelling aqueous systems. Adjusting the concentration of the polymer, provides the desired sol-gel transition, that is, the lower the concentration of polymer, the higher the sol-gel transition temperature.

In U.S. Pat. Nos. 4,474,751; 752; 753; and 4,478,822, drug delivery systems are described which utilize thermosetting polyoxyalkylene gels; the unique feature of these systems is that both the gel transition temperature and/or the rigidity of the gel can be modified by adjustment of the ionic strength, as well as by the concentration of the polymer.

Other patents disclosing pharmaceutical compositions which rely upon an aqueous gel composition as a vehicle for the application of the drug or cosmetic preparation are U.S. Pat. Nos. 4,883,660; 4,861,760; 4,810,503; 4,767,619; and 4,511,563.

Steinleitner et al in an article entitled, "Poloxamer 407 as an Intraperitoneal Barrier Material for the Prevention of Post-Surgical Adhesion Formation and Reformation in Rodent Models for Reproductive Surgery, Obstetrics and Gynecology, volume 1, pages 48-52, 1991, discloses the anti-adhesion properties of poloxamer 407. Poloxamer 407 is a biocompatable polymer, the viscosity of which is dependent upon temperature and concentration in aqueous solutions. The material is a liquid at room temperature and is a solid at body temperature. In one experiment, poloxamer solutions in concentrations ranging from 15-35% were applied to standardized lesions on the uterine horn of hamsters. Significant reduction in post-traumatic adhesion formation was observed following treatment with the poloxamer solutions. In a second experiment, the polymer was used in a paradigm for a typical situation encountered in fertility surgery, that is, the prevention of adhesion reformation after lysis of established adhesions. The effects of applying poloxamer 407 after adhesiotomy in rabbits was compared to controls that had received no treatments. The adhesion reformation was reduced by a poloxamer 407 treatment.

Steinleitner in an article entitled, "New Modalities Under Development for Adhesion Prevention; "Immunomodulatory Agents and Poloxamer Barrier Materials", Gynecologic Surgery and Adhesion Prevention, pages 235-251, 1993 discloses a review of the pathophysiology of peritoneal wound repair that summarizes studies evaluating immunomodulatory agents designed to favorably influence aspects of post surgical healing. Besides describing the physiology of peritoneal repairs, the authors of the studies list a number of immunomodulatory agents used in adhesion prevention such as calcium channel blocking agents and other agents such as pentoxifylline. The authors emphasize the application of barrier materials to effect physical separation of injured viscera stating that it may be the most effective therapy currently available to surgeons. The ideal barrier material should be biocompatible, be absorbable and have a neutral or beneficial effect on the events of peritoneal healing. Further, the barrier material should serve as a local delivery system for pharmacologic anti-adhesion treatments. Poloxamer 407 has been identified as particularly well suited for use in preventing adhesion formation or reformation as a barrier material in infertility surgery.

The Steinleitner review discloses the use of pentoxifylline in preventing the formation of post surgical adhesions. Pentoxifylline is a methylxanthine derivative which improves the flow properties of blood by decreasing its viscosity. In patients with chronic peripheral arterial disease, pentoxifylline increases blood flow to the affected microcirculation and enhances tissue oxygenation. Steinleitner et al. used the hamster uterine horn primary injury model and administered doses of 0.1 to 10 mg\kg subcutaneously at 12 hour intervals. This regimen was found to provide protection against post-traumatic adhesion formation.

While the prior art discloses the use of pentoxifylline and poloxamer 407 separately as agents that may be useful in inhibiting or reducing the formation/reformation of adhesions in the peritoneal cavity for mammals, there is a need for an improved composition that can be applied directly to the body cavity and a process for reducing post surgical adhesion formation/reformation.

SUMMARY OF THE INVENTION

Polyoxyalkylene compositions, pentoxifylline, and a method of use are disclosed for inhibiting post surgical adhesion formation/reformation in mammals following injury to the organs of a body cavity. The compositions of the invention are also useful in reducing adhesion formation/reformation in body cavities. The useful compositions comprise a combination of pentoxifylline and a polyether and surfactant or pentoxifylline and polyoxyalkylene block copolymer.

Polyphase systems are also useful and may contain non-aqueous solutes, non-aqueous solvents, and other non-aqueous additives. Homogeneous, polyphase systems can contain such additives as water insoluble high molecular weight fatty acids and alcohols, fixed oils, volatile oils and waxes, mono, di, and triglycerides, and synthetic, water insoluble polymers without altering the functionality of the system. In one embodiment of the invention, the concentration of the block copolymer in the compositions of the invention can be adjusted to take advantage of the gelation properties of certain polyoxyalkylene block copolymers. For instance, aqueous solutions of said block copolymers at certain concentrations form clear gels at mammalian body temperatures but are liquids at ambient temperatures. The aqueous solutions of said block copolymers can be provided as isomotically and pH balanced compositions which match the pH and osmotic pressure of mammalian bodily fluids. Subsequent to deposition of the compositions of the invention on the tissues of the peritoneal, pelvic, or pleural cavity of a mammal, or other body spaces, as described above, the polyoxyalkylene block copolymer is absorbed into the circulatory system and is eventually excreted, mainly in the urine. In another embodiment of the invention aqueous gels are produced by combination of an alpha-olefin epoxide capped polyether and a surfactant as described in U.S. Pat. No. 4,810,503. In this embodiment, the aqueous, osmotically balanced gels are applied as gels to injured tissues in the peritoneal, pelvic or pleural cavities or other body spaces with pentoxifylline to inhibit post-surgical adhesion formation/reformation.

In addition to functioning as a means of reducing post-operative adhesion formation/reformation in mammals following surgical or accidental injury or inflammation to the peritoneal, pelvic or pleural cavity or other body spaces, the pentoxifylline and polyoxyalkylene compositions provide an osmotically balanced environment surrounding the surgical injury which reduces adhesion formation/reformation. For instance, the polyoxyalkylene block copolymer and pentoxifylline can be instilled within the uterine cavity as a distending medium during diagnostic or operative intrauterine endoscopic procedures. This procedure has two advantages. First, since certain aqueous concentrations of the preferred polyoxyalkylene block copolymers form a clear gel, their use is well suited for visualization of the tissues within the uterine cavity. Second, since these aqueous solutions are liquids at room temperature and below and form a clear gel at body temperature, the use of said solutions to separate the uterine cavity walls will diminish or prevent post-surgical adhesion formation. Similarly, the application of the aqueous, polyoxyalkylene, pentoxifylline, capped polyether-surfactant combination as gels provide a similar adhesion reducing effect.

DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates pentoxifylline release from formulations of carboxymethylcellulose, hydroxyethylcellulose, sodium alginate, xanthan gum, and phosphate buffer (vehicle control).

FIG. 2 illustrates pentoxifylline release from formulations of low MW hyaluronic acid, high MW hyaluronic acid, collagen, and phosphate buffer (vehicle control).

FIG. 3 illustrates pentoxifylline release formulations from PEG 8000, 14% poloxamer 407 with 20 mg/ml pentoxifylline, PEG 8000, 14% poloxamer 407 with 20 mg/ml pentoxifylline, 14% poloxamer 407 with 24 mg/ml pentoxifylline, and 16% poloxamer 188 with 12 mg/ml pentoxifylline, and phosphate buffer (vehicle control).

FIG. 4 illustrates pentoxifylline release from formulations of 28% poloxamer 407 with 12 mg/ml pentoxifylline, 14% poloxamer 407 with 36 mg/ml pentoxifylline and 14% poloxamer 407 with 12 mg/ml penoxifylline.

DETAILED DESCRIPTION OF THE INVENTION

A process and composition are disclosed for inhibiting post-operative adhesion formation/reformation in mammals following surgical or accidental injury or inflammation to the organs of the peritoneal or pleural cavity or other body spaces. In this specification and claims, the terms "peritoneal" and "abdominal" cavity are used as synonyms, as are the terms "pleural" and "thoracic" cavity. By the term "body spaces", we mean cavities or areas of the body where there is an environment for allowing the composition of the present invention to be in contact with body tissues. "Body spaces" may be further defined as peritoneal, abdominal, and thoracic cavities as well as joints and areas of the body containing synovial fluid. The compositions include pentoxifylline, which is a methylxanthine derivative, and indicated for the treatment of patients with intermittent claudication on the basis of chronic occlusive arterial disease of the limbs.

The present invention discloses a novel use for pentoxifylline, in effective amounts, in combination with the polyoxyalkylene compositions disclosed herein, by providing for the inhibition of post surgical adhesion formation/reformation when applied directly onto a body tissue following injury.

In one embodiment of the invention, the preferred aqueous, polyoxyalkylene block copolymer compositions are prepared at concentrations so as to take advantage of the gelation properties of certain of said block copolymers and at a pH and osmotic pressure which match that of bodily fluids (pH 7.4 and 290 mOsm/kg). When certain of the polyoxyalkylene block copolymers of the invention are present in aqueous solutions at concentrations preferably of about 5% to about 30% by weight such compositions can provide liquid compositions at ambient temperatures or below which revert to gel compositions upon contact with living mammalian tissue.

Alternatively, useful compositions of the invention include aqueous compositions comprising at least one polyoxyalkylene block copolymer which do not form gels at mammalian body temperature as well as aqueous, isotonic, polyoxyalkylene gel polymers comprising an alpha olefin epoxide capped polyether and a surfactant. It is believed that the aqueous compositions of the invention which do not form gels upon contact with living mammalian tissue as well as those which are applied to mammalian tissue in the gel state, also function to prevent the formation/reformation of adhesions subsequent to surgical procedures incurred by a mechanism of action which has been termed in the prior art "hydroflotation". Thus the injured tissues are prevented from contacting adjacent tissues by the means of the inclusion of a foreign fluid or gel in the peritoneal, pelvic, or pleural cavity or other body spaces. It is believed that the mechanism of action to prevent the formation/reformation of adhesions is, in addition to hydroflotation, properly characterized as the result of separating the adjacent mammalian tissues by a firm, adherent coating.

The polyoxyalkylene block copolymer compositions of one embodiment of the invention include at least one block copolymer as defined below, in combination with pentoxifylline. The copolymer is applied to injured tissue in combination with pentoxifylline, both in effective amounts. The block copolymer compositions of the invention comprise at least one polyoxyalkylene block copolymer of the formula:

    Y[(A.sub.n --E--H].sub.x                                   (I)

wherein A is a polyoxyalkylene moiety having an oxygen/carbon atom ration of less than 0.5, x is at least 1, Y is derived from water or an organic compound containing x reactive hydrogen atoms, E is a polyoxyalkylene moiety constituting at least about 60% by weight of the copolymer, n has a value such that the average molecular weight of A is at least about 500 to about 900, as determined by the hydroxyl number of a hydrophobe base intermediate,

    Y[(A.sub.n --H].sub.x                                      (II)

and the total average molecular weight of the copolymer is at least about 5000.

In addition to those polyoxyalkylene polymers described above, which are suitable in combination with effective amounts of pentoxifylline in the formation of the compositions of the invention, other polyoxyalkylene polymers which form gels at low concentrations in water are suitable. These are described in U.S. Pat. No. 4,810,503, incorporated herein by reference. These polymers are prepared by capping conventional polyoxyalkylene polyether polyols with an alpha-olefin epoxide having an average of about 20 to about 45 carbon atoms, or mixtures thereof. Aqueous solutions of these polymers gel in combination with surfactants, which can be ionic or nonionic. The combination of the capped polyether polymers and the surfactants provide aqueous gels at low concentrations of the capped polymer and surfactant which generally do not exceed 10% by weight total. Detailed methods of preparing these aqueous gels are disclosed in U.S. Pat. No. 4,810,503. Preparation of said aqueous gels is generally described below. Preferred surfactants for use in preparing these gels are also disclosed in said patent.

A conventional copolymer polyether polyol is prepared by preparing block or heteric intermediate polymers of ethylene oxide and at least one lower alkylene oxide having 3 to 4 carbon atoms as intermediates. These are then capped with the alpha-olefin epoxide to prepare the polymers of this invention. Ethylene oxide homopolymers capped with said alpha-olefin oxides are also useful as intermediates.

The heteric copolymer intermediate is prepared by mixing ethylene oxide and at least one lower alkylene oxide having 3 to 4 carbon atoms with a low molecular weight active hydrogen-containing compound initiator having at least two active hydrogens and preferably, 2 to 6 active hydrogen atoms such as a polyhydric alcohol, containing from 2 to 10 carbon atoms and from 2 to 6 hydroxyl groups, heating said mixture to a temperature in the range of about 50° C. to 150° C., preferably, from 80° C. to 130° C., under an inert gas pressure, preferably, from about 30 psig to 90 psig.

A block copolymer intermediate is prepared by reacting either the ethylene oxide or said alkylene oxide having 3 to 4 carbon atoms with said active hydrogen-containing compound followed by reaction with the other alkylene oxide. The ethylene oxide and the alkylene oxides having from 3 to 4 carbon atoms are used in said intermediates in amounts so that the resulting polyether product will contain at least 10 percent by weight, preferably about 60 percent to about 80 percent by weight, ethylene oxide residue. The ethylene oxide homopolymer intermediate is prepared by reacting ethylene oxide with said active hydrogen-containing compound. The reaction conditions for preparing the block copolymer and ethylene oxide homopolymer intermediates are similar to those for the heteric copolymer intermediate. The temperature and pressure are maintained in the above ranges for a period of about one hour to ten hours, preferably one to three hours.

The alpha-olefin oxides which are utilized to modify the conventional polyether intermediate of the prior art are those oxides and the commercially available mixtures thereof generally containing an average of about 20 to 45, preferably about 20 to 30, carbon atoms. The amount of alpha-olefin required to obtain the more efficient capped polyethers is generally about 0.3 to 10 percent, preferably about 4 to 8 percent, of the total weight of the polyethers of the invention

Since the preparation of heteric and block copolymers of alkylene oxides and ethylene oxide homopolymers are well known in the art, further description of the preparation of said polymers is unnecessary. Further details of the preparation of heteric copolymers of lower alkylene oxides can be obtained in U.S. Pat. No. 3,829,506, incorporated herein by reference. Further information on the preparation of block copolymers of lower alkylene oxides can be obtained in U.S. Pat. Nos. 3,535,307; 3,036,118; 2,979,578; 2,677,700; and 2,675,619 incorporated herein by reference.

The surfactants may be ionic or non-ionic and many surfactants and types of surfactants may be employed. While all surfactants may not be effective in the preparation of osmotically balanced gels of the instant invention, the fact that many are effective makes it a simple matter for one skilled in the art to select such surfactant with a minimum of trial and error.

The amounts of capped polyether polymer and surfactant may be as little as 1.0 percent by weight or less of each depending on the type and amount of the other components. There appears to be no maximum amount of either component than that dictated by solubility and preferred osmolality in an aqueous solution. However, the total amount of capped polymer and surfactant would generally not exceed 10 percent by weight.

Preferably, the block copolymers which are useful are selected from those defined above in formula I which contain at least about 60% by weight, preferably at least about 70%, by weight of the residue of ethylene oxide (polyoxyethylene moiety). Said copolymers have a total average molecular weight of at least about 5000, and form a gel at mammalian body temperature, when in an aqueous solution at a concentration generally, of about 10 to about 40%, and preferably, about 15 to about 30% by weight.

The amount of pentoxifylline used is an amount effective to inhibit adhesion formation/reformation in combination with the block copolymers of this invention when applied as a liquid or gel to a body cavity following surgery. Typically, the amount may be about 0.05% to about 7.0% by weight, preferably about 1.0% to about 4.0% by weight, based upon the total weight of the compositions of the invention.

The proportion of water used is about 60% to about 90%, by weight, preferably, about 70% to about 85%, by weight based upon the total weight of the composition of the invention. Useful polyoxyalkylene block copolymers which will form gels in such aqueous solutions can be prepared using a hydrophobe base (such as A in Formulas I and II) derived from propylene oxide, butylene oxide, or mixtures thereof. These block copolymers and representative methods of preparation are further generally described in U.S. Pat. Nos. 2,677,700; 2,674,619; and U.S. Pat. No. 2,979,528, incorporated herein by reference.

Generally, the polyoxybutylene-based block copolymers useful in the compositions of the invention are prepared by first condensing 1,2 butylene oxide with a water soluble organic compound initiator containing 1 to about 6 carbon atoms such as 1,4 butylene glycol or propylene glycol and at least 2 reactive hydrogen atoms to prepare a polyoxyalkylene polymer hydrophobe of at least about 500, preferably at least about 1000, most preferably at least about 1500 average molecular weight. Subsequently, the hydrophobe is capped with an ethylene oxide residue. Specific methods for preparing these compounds are described in U.S. Pat. No. 2,828,345 and British Patent No. 722,746, both of which are hereby incorporated by reference.

Useful polyoxybutylene based block copolymers conform to the following generic formula:

    HO(C.sub.2 H.sub.4 O).sub.b (C.sub.4 H.sub.8 O).sub.a (C.sub.2 H.sub.4 O).sub.b H                                                (III)

wherein a is an integer such that the hydrophobe base represented by (C₄ H₈ O) a has a molecular weight of at least about 500, preferably at least about 1000 and most preferably at least about 4000, as determined by hydroxyl number, the polyoxyethylene chain constituting at least about 60%, preferably at least about 70% by weight of the copolymer, and the copolymer having a total average molecular weight of at least about 5000, preferably at least about 10,000.

The copolymer is characterized in that all the hydrophobic oxybutylene groups are present in chains bonded to an organic radical at the former site of a reactive hydrogen atom thereby constituting a polyoxybutylene base copolymer. The hydrophilic oxyethylene groups are used to cap the polyoxybutylene base polymer.

Polyoxyethylene-polyoxypropylene block copolymers which can be used to form aqueous gels can be represented by the following formula:

    HO(C.sub.2 H.sub.4 O).sub.b (C.sub.3 H.sub.6 O).sub.a (C.sub.2 H.sub.4 O).sub.b H                                                (IV)

wherein a is an integer such that the hydrophobe base represented by (C₃ H₆ O) has a molecular weight of at least about 900, preferably at least about 2500 average molecular weight, as determined by hydroxyl number; the polyoxyethylene chain constituting at least about 60%, preferably at least about 70% by weight of the copolymer, and the copolymer having a total average molecular weight of at least about 5000, preferably at least about 10,000.

Polyoxyethylene-polyoxypropylene block copolymer adducts of ethylenediamine which can be used may be represented by the following formula: ##STR1## wherein a and b are integers such that the copolymer may have (1) a hydrophobe base molecular weight of at least about 2000, preferably at least about 3000, and most preferably at least about 4500, (2) a hydrophile content of at least about 60%, preferably at least about 70% by weight, and (3) a total average molecular weight of at least about 5000, preferably at least about 10,000.

The hydrophobe base of the copolymer of formula V is prepared by adding propylene oxide for reaction at the site of the four reactive hydrogen atoms on the amine groups of ethylenediamine. An ethylene oxide residue is used to cap the hydrophobe base. These hydrophile polyoxyethylene groups are controlled so as to constitute about 60% to about 80% by weight of the copolymer.

The procedure used to prepare aqueous solutions which form gels of the polyoxyalkylene block copolymers is well known. Either a hot or cold process for forming the solutions can be used. A cold technique involves the steps of dissolving the polyoxyalkylene block copolymer at a temperature of about 5° C. to about 10° C. in water. When solution is complete the system is brought to room temperature whereupon it forms a gel. If the hot process of forming the gel is used the polymer is added to water heated to a temperature of about 75° C. to about 85° C. with slow stirring until a clear homogeneous solution is obtained. Upon cooling, a clear gel is formed. Block copolymer gels containing polyoxybutylene hydrophobes must be prepared by the above hot process, since these will not liquify at low temperatures.

As used herein, the term "gel" is defined as a solid or semisolid solution containing a certain quantity of water. The solution with water is often called a "hydrogel".

The organic compound initiator which is utilized in the process for the preparation of the polyoxyalkylene block copolymers generally is water or an organic compound and can contain a plurality of reactive hydrogen atoms. Preferably, Y in formulas I and II above is defined as derived from a water soluble organic compound having 1 to about 6 carbon atoms and containing x reactive hydrogen atoms where x has a value generally, of at least 1, preferably, a value of at least 2. Y is derived from water soluble organic compounds having at least two reactive hydrogen atoms. Falling within the scope of the compounds of the present invention are water soluble organic compounds such as propylene glycol, glycerin, pentaerythritol, trimethylolpropane, ethylenediamine, and mixtures hereof and the like.

The polyoxypropylene chains can optionally contain small amounts of at least one of polyoxyethylene or oxybutylene groups. Polyoxyethylene chains can optionally contain small amounts of at least one of oxypropylene oxybutylene groups. Polyoxybutylene chains can optionally contain small amounts of at least one of polyoxyethylene or polyoxypropylene groups. The physical form of the polyoxyalkylene block copolymers can be a viscous liquid, a paste, or a solid granular material depending upon the molecular weight of the polymer. Useful polyoxyalkylene block copolymers generally have a total average molecular weight of about 5000 to about 50,000, preferably about 5,000 to about 35,000 and most preferably about 10,000 to about 25,000.

Preferably the polyoxyalkylene block copolymer is applied to surgically injured tissue as an aqueous solution which upon contact with living mammalian tissue forms an adherent coating. Where a polyoxyalkylene block copolymer is a viscous liquid or paste, the compositions can be applied without dilution to areas of surgical injury in the abdominal or thoracic cavities. The aqueous solution or viscous liquid or paste may be applied to form an adherent coating with the body tissue in the body cavity to aid in the inhibition of the formation or reformation of adhesions. Another function is to deliver pentoxifylline to the site of treatment. Serving as a barrier, the composition of the present invention prevents the close proximity or contact of tissues between surfaces of which adhesions would form.

The following examples illustrate the various aspects of the invention but are not intended to limit its scope. Where not otherwise specified throughout this specification and claims, temperatures are given in degrees centigrade, and parts, percentages, and proportions are by weight.

EXAMPLE 1

An aqueous solution was made of a polyoxyethylene-polyoxypropylene block copolymer having the structure generically shown as formula IV and having a polyoxypropylene hydrophobe base average molecular weight of about 4000, a total average molecular weight of about 11,500, and containing oxyethylene groups in the amount of at least about 70% by weight of the total weight of copolymer. This copolymer is sold under the trademark PLURONIC® F-127 by the BASF Corporation, Parsippany, N.J. (also known as Poloxamer 407). A solution was made by dissolving said polymer in cold (4° C.) distilled water to give a concentration of approximately 30% by weight in accordance with the cold process described above for forming aqueous solutions. More specific solution procedures are described in "Artificial Skin I Preparation and Properties of Pluronic F-127 Gels for Treatment of Burns", J. Biomed. Mater. Res. 6, 527, 1972, incorporated herein reference. The block copolymer has the formula: ##STR2##

This solution is a liquid at 40° C. and forms a gel which is adherent to living tissue upon contact.

                  EXAMPLE 2                                                        ______________________________________                                         The following formation was prepared:                                              INGREDIENT        PERCENT BY WEIGHT                                        ______________________________________                                         Poloxamer 407, NF 28.00                                                          Pentoxifylline 0.40                                                            Tromethamine (TRIS), USP 0.1091                                                Maleic Acid 0.1045                                                             Sodium Hydroxide pellets, USP 0.0420                                           Sterile Water for Irrigation, USP 71.344                                     ______________________________________                                    

First, the water was weighed in a tared vessel. Second, the tromethamine, maleic acid and sodium hydroxide were added to the water and mixed for twenty minutes. The pH and osmolality of the solution were tested and found to be 7.6 and 39 Mosm/Kg, respectively. The solution was cooled to 6° C. and the poloxamer was added to the solution over a two hour period with constant stirring. The solution was stored under a nitrogen atmosphere at 4° C. for fifteen hours to effect a reduction in the foam content of the solution. The solution was tested for Ph, osmolality, and viscosity and the results were 7.4, 123 mOsm/kg and 360,000 centipoise at 30° C., respectively. The solution was packaged into 30 cc serum vials, capped with rubber stoppers and sterilized with steam at 121° C. and 15 psi for twenty minutes. To each vial, an amount of pentoxifylline was added via sterile filtration, such that a final concentration of 4 milligrams of pentoxifylline per milliliter of solution was obtained. Each vial was recapped and sealed as soon as the addition of pentoxifylline was completed, then cooled to 4° C. and mixed for ten minutes to ensure uniform distribution of pentoxifylline in the vial.

EXAMPLE 3 Analytical Method Measurement of Pentoxifylline Release from Various Formulations

Approximately 15 cm of SpectraPor regenerated cellulose dialysis tubing (6000-8000 molecular weight cut off, cat. #132650, Source: Spectrum Medical Industries, Inc.) is rinsed in distilled water to remove preservatives. One end is sealed with the appropriate sized closure.

5 ml of the formulation to be tested was placed in the tubing and the other end sealed as close as possible to the sample. The tubing is placed in a beaker containing 95 ml of phosphate buffer (0.05 M KH₂ PO₄ +0.0391 M NaOH, pH 7.4) and a magnetic stirring bar. The solution was mixed on low speed at room temperature. One ml samples were withdrawn (via pipet) at each time point and diluted to an appropriate volume (either 10 or 25 ml) with water for UV absorbance measurements.

UV absorbance of the test solution is determined at 273 nm versus a water blank. A 100% release standard is prepared by diluting 5 ml of the formulation to be tested to 100 ml with phosphate buffer. 1 ml of this solution is then diluted to 25 ml with water for absorbance measurement.

Percent released is calculated by ratioing the absorbance of the test solution at each time point against the 100% release standard, taking into account any differences in dilution, the small decrease in volume of the test solution at each time point caused by earlier sample withdrawals and the amount of pentoxifylline already removed due to previous samplings.

The results are summarized in FIGS. 1-4. FIG. 1 illustrates pentoxifylline release from formulations of carboxymethylcellulose, hydroxyethylcellulose, sodium alginate, xanthan gum, and phosphate buffer (vehicle control). FIG. 2 illustrates pentoxifylline release from formulations of low MW hyaluronic acid, high MW hyaluronic acid, collagen, and phosphate buffer (vehicle control). FIG. 3 illustrates pentoxifylline release formulations from PEG 8000, 14% poloxamer 407 with 20 mg/ml pentoxifylline, PEG 8000, 14% poloxamer 407 with 20 mg/ml pentoxifylline, 14% poloxamer 407 with 24 mg/ml pentoxifylline, and 16% poloxamer 188 with 12 mg/ml pentoxifylline, and phosphate buffer (vehicle control). FIG. 4 illustrates pentoxifylline release from formulations of 28% poloxarer 407 with 12 mg/ml pentoxifylline, 14% poloxamer 407 with 36 mg/ml pentoxifylline and 14% poloxamer 407 with 12 mg/ml penoxifylline.

    ______________________________________                                         Representative Formulations                                                        Ingredient        Source   Weight %                                        ______________________________________                                         Formulation: Sodium Alginate Gel with Pentoxifylline                               Sodium Alginate   TIC Gums 2.000                                             Pentoxifylline ICN 1.200                                                       Tromethamine USP Spectrum 0.109                                                Maleic Acid Spectrum 0.105                                                     Sodium Hydroxide, USP Spectrum 0.042                                           Purified Water Bamsted 96.544                                                Formulation: Collagen Gel with Pentoxifylline                                      Hydracol Soluble Collagen                                                                        Gattefasse                                                                              1.000                                             Pentoxifylline ICN 1.200                                                       Tromethamine USP Spectrum 0.109                                                Maleic Acid Spectrum 0.105                                                     Sodium Hydroxide, USP Spectrum 0.042                                           Purified Water Bamsted 97.540                                                Formulation: Vehicle control with Pentoxifylline                                   Pentoxifylline    ICN      1.200                                             Tromomethamine USP Spectrum 0.109                                              Maleic Acid Spectrum 0.105                                                     Sodium Hydroxide, USP Spectrum 0.042                                           Sodium Chloride Spectrum 0.750                                                 Purified Water Bamsted 97.794                                                Formula: PEG 8000 with Pentoxifylline                                              PEG 8000          Union    10.000                                             Carbide                                                                       Pentoxifylline ICN 1.200                                                       Tromethamine USP Spectrum 0.109                                                Maleic Acid Spectrum 0.105                                                     Sodium Hydroxide, USP Spectrum 0.042                                           Purified Water Bamsted 88.544                                                Formula: 14% Poloxamer 407 with 20 mg/ml Pentoxifylline                            Polaxmer 407      BASF     14.000                                            Pentoxifylline ICN 2.000                                                       Tromethamine USP Spectrum 0.109                                                Maleic Acid Spectrum 0.105                                                     Sodium Hydroxide, USP Spectrum 0.042                                           Sodium Chloride Spectrum 0.040                                                 Purified Water Bamsted 83.700                                                Formula: 14% Poloxamer 407 with 24 mg/ml Pentoxifylline                            Poloxamer 407     BASF     14.000                                            Pentoxifylline ICN 2.400                                                       Tromethamine USP Spectrum 0.109                                                Maleic Acid Spectrum 0.105                                                     Sodium Hydroxide, USP Spectrum 0.042                                           Sodium Chloride Spectrum 0.020                                                 Purified Water Bamsted 83.324                                                Formula: 16% Poloxamer 188 with 12 mg/ml Pentoxifylline                            Poloxamer 188     BASF     16.000                                            Pentoxifylline ICN 1.200                                                       Tromethamine USP Spectrum 0.109                                                Maleic Acid Spectrum 0.105                                                     Sodium Hydroxide, USP Spectrum 0.042                                           Purified Water Bamsted 82.544                                                Formula: 28% Poloxamer 407 with 12 mg/ml Pentoxifylline                            Poloxamer 407     BASF     28.00                                             Pentoxifylline ICN 1.20                                                        Tromethamine, USP Spectrum 0.109                                               Maleic Acid Spectrum 0.105                                                     Sodium Hydroxide, USP Spectrum 0.042                                           Purified Water Bamsted 70.544                                                Formula: 14% Poloxamer 407 with 36 mg/ml Pentoxifylline                            Poloxamer 407     BASF     14.00                                             Pentoxifylline ICN 3.60                                                        Tromethamine, USP Spectrum 0.109                                               Maleic Acid Spectrum 0.105                                                     Sodium Hydroxide, USP Spectrum 0.042                                           Purified Water Bamsted 82.144                                                Formula: 14% Poloxamer 407 with 12 mg/ml Pentoxifylline                            Poloxamer 407     BASF     14.00                                             Pentoxifylline ICN 1.20                                                        Tromethamine, USP Spectrum 0.109                                               Maleic Acid Spectrum 0.105                                                     Sodium Hydroxide, USP Spectrum 0.042                                           Sodium Chloride Spectrum 0.040                                                 Purified Water Bamsted 84.504                                                ______________________________________                                    

                  EXAMPLE 4                                                        ______________________________________                                         Surgical Trial on Prospective Study                                              on Adhesions in the Rabbit Model                                               To assess the potential of poloxamer 407 with pentoxifylline to prevent       or reduce adhesions the following experiment was performed.                    Preparation of 14% poloxamer 407 with 1.2% pentoxifylline solution.               INGREDIENT        PERCENT BY WEIGHT                                        ______________________________________                                         Poloxamer 407, NF 14.00                                                          Pentoxifylline 1.20                                                            Tromethamine (TRIS), USP 0.1091                                                Maleic Acid 0.1045                                                             Sodium Hydroxide pellets, USP 0.0420                                           Sodium Chloride, USP 0.04                                                      Sterile Water for Irrigation, USP 82.54                                      ______________________________________                                    

Water was weighed into a tared vessel. Pentoxifylline, tromethamine, maleic acid and sodium hydroxide were added to the water and mixed for twenty minutes. The pH and osmolality of the solution were tested and found to be 7.6 and 109 mOsm/Kg, respectively. The solution was cooled to 6° C. and the poloxamer was added to the solution over a two hour period with constant stirring. The solution was stored under a nitrogen atmosphere at 4° C. for fifteen hours to effect a reduction in the foam content of the solution. The solution was tested for pH and osmolality and the results were 7.4 and 290 mOsm/Kg, respectively. The solution was packaged into 30 cc serum vials, capped with rubber stoppers and sterilized with steam at 121° C. and 15 psi for twenty minutes. The vials were cooled to 4° C. and swirled for ten minutes to ensure uniform distribution.

The experiment utilized eighteen, healthy, female, New Zealand White rabbits. The uterine horn was exteriorized then abraded by scraping 20-30 times with a no. 10 scalpel blade until a wound was produced that had punctate bleeding. Nine of the rabbits received 3.0 ml of 14% poloxamer 407 with 1.2% pentoxifylline delivered at 0° C. Five rabbits received a physiologic buffer also delivered at 0° C. Four rabbits received no treatment. The opposite uterine horn was untreated. The uterine horns were returned to the peritoneal cavity and the incision was closed. On the 12th day after the initial surgery, the animals were necropsied and the adhesions were scored. The adhesions were scored as follows: 0=no adhesions, 1=adhesions up to 25% of area, 2=adhesions from 25% to 50 % of area, 3=greater than 50% of area, 4=100% adhesions.

    ______________________________________                                         Treatment        Adhesion Score (Mean)                                         ______________________________________                                         14% poloxamer 407 with 12%                                                                      0.67                                                            pentoxifylline                                                                 physiologic buffer 2.4                                                         no treatment 2.35                                                            ______________________________________                                    

    ______________________________________                                         Preparation of poloxamer 188 solution                                              Ingredient         Percent by Weight                                       ______________________________________                                         Poloxamer 188, NF  16.00                                                         Pentoxifylline 1.20                                                            Tromethamine (TRIS), USP 0.1091                                                Maleic Acid 0.1045                                                             Sodium Hydroxide pellets, USP 0.0420                                           Sterile Water For Irrigation, USP 82.54                                      ______________________________________                                    

Water was weighed into a tared vessel. Pentoxifylline, tromethamine, maleic acid and sodium hydroxide were added to the water and mixed for twenty minutes. The pH and osmolality of the solution were tested and found to be 7.7 and 50 mOsm/Kg, respectively. The solution was cooled to 6° C. and the poloxamer was added to the solution over a two hour period with constant stirring. The solution was stored under a nitrogen atmosphere at 4° C. for fifteen hours to effect a reduction in the foam content of the solution. The solution was tested for pH and osmolality and the rabbits were 7.4 and 140 mOsm/Kg, respectively. The solution was packaged into 30 cc serum vials, capped with rubber stoppers and sterilized with steam at 121° C. and 15 psi for twenty minutes. The vials were cooled to 4° C. and swirled for ten minutes to ensure uniform distribution of pentoxifylline in the vial.

EXAMPLE 5 Surgical Trial and Prospective Study on Adhesions in the Porcine Model

The purpose of this procedure is to evaluate the surgical performance of laparoscopic pelvic and lower para-aortic lymphadenectomy and to study the postoperative adhesion formation in a randomized trial, using an adhesion prevention adjuvant containing poloxamer with or without pentoxifylline.

Under general anesthesia twenty-eight female piglets underwent video-endoscopic transperitoneal lymphadenectomy. On each side, four lymph node sites were identified: obdurator fossa, external iliac, para-aortic and internal iliac. These sites were defined by consistent anatomical borders. The lymph nodes were surgically removed and hemostasis obtained. All sites on one side, selected randomly, were treated with the formulation described in Example 2, a buffered, osmotically balanced formulation of 28% poloxamer 407 or control buffer. The sites on the contralateral side were left untreated.

After 14 days, a laparotomy was performed to evaluate healing and adhesion formation at the sites of lymph node removal.

Evaluation of Type of Adhesions

Slides/photos were taken, and a score was made. An independent observer, unaware of the previous procedure was used to assess the adhesions, in accordance with the procedure described by Shimanuk, T, et al, J Biomed Mater Res. 22, 173-185 (1987), shown in Table 1 as follows:

    ______________________________________                                         Grade   Points      Description                                                ______________________________________                                         0       0           No adhesions                                                 1 1 Avascular, is easily lysed but fails                                         to bleed.                                                                    2 3 Vascular, is easily lysed but bleeds                                         at time of lysis.                                                            3 5 Thick, requires extensive sharp                                              surgical dissection.                                                       ______________________________________                                    

The total score was calculated the following way: the assigned points for each adhesion grade were multiplied by the percentage of the surface (0.00-1.00) area involved with that specific type of adhesion. Statistical analysis was performed using the Wilcoxon signed rank test.

The results are shown in Table 2. At the same volume, formulation with pentoxifylline reduced adhesions significantly at all 4 sites when compared to control in the animals tested.

Formulations containing poloxamer 407 without pentoxifylline reduced adhesions formation at all surgical sites, but the reduction was statistically significant only at the internal iliac site.

While this invention has been described with reference to certain specific embodiments, it will be recognized by those skilled in the art that many variations are possible without departing from the scope and spirit of the invention, and it will be understood that it is intended to cover all changes and modifications of the invention, disclosed herein for the purposes of illustration, which do not constitute departures from the spirit and scope of the invention.

                                      TABLE 2                                      __________________________________________________________________________                             14% Polyoxamer 407 with                                    4 mg/ml                                                                      Vehicle Control 14% Poloxamer 407 pentoxifylline                             Treated                                                                              Control                                                                              Treated                                                                              Control                                                                              Treated                                                                              Control                                          __________________________________________________________________________     Obduratur                                                                      Mean                                                                              1.37                                                                              Mean                                                                              1.47                                                                              Mean                                                                              0.72                                                                              Mean                                                                              0.66                                                                              Mean                                                                              0.60                                                                              Mean                                                                              1.26                                            S.D. 0.61 S.D. 0.61 S.D. 0.61 S.D. 0.70 S.D. 0.41 S.D. 0.73                  Internal                                                                       Mean                                                                              1.33                                                                              Mean                                                                              1.93                                                                              Mean                                                                              0.78                                                                              Mean                                                                              1.80                                                                              Mean                                                                              0.51                                                                              Mean                                                                              1.20                                            S.D. 1.00 S.D. 1.22 S.D. 0.60 S.D. 0.97 S.D. 0.36 S.D. 0.91                  External                                                                       Mean                                                                              2.25                                                                              Mean                                                                              1.84                                                                              Mean                                                                              0.83                                                                              Mean                                                                              1.27                                                                              Mean                                                                              0.68                                                                              Mean                                                                              1.87                                            S.D. 0.98 S.D. 0.83 S.D. 0.52 S.D. 0.88 S.D. 0.45 S.D. 0.73                  Paraortic                                                                      Mean                                                                              1.58                                                                              Mean                                                                              1.62                                                                              Mean                                                                              0.77                                                                              Mean                                                                              1.15                                                                              Mean                                                                              0.95                                                                              Mean                                                                              1.64                                            S.D. 0.83 S.D. 0.66 S.D. 0.53 S.D. 0.79 S.D. 0.85 S.D. 0.75                  __________________________________________________________________________ 

What we claim:
 1. A method of inhibiting the formation/reformation of internal adhesions comprising applying to one or more tissues of a mammal in need thereof an aqueous composition comprising:(1) an effective amount of pentoxifylline (2) about 60% to about 90% by weight of water, and; (3) about 5% to about 35% by weight of a polyoxyalkylene block copolymer of the formula

    (Y[(A).sub.n --E--H).sub.x                                 (I)

wherein A is a polyoxyalkylene moiety having an oxygen/carbon atom ratio of less than 0.5, x is at least 1, Y is derived from water or an organic compound containing x reactive hydrogen atoms, E is a polyoxyethylene moiety, n has a value such that the minimum molecular weight of A is between about 500 and about 900, as determined by the hydroxyl number of an intermediate of the formula

    Y((A)--H).sub.x                                            (II)

and the total average molecular weight of the polyoxyalkylene block copolymer is at least about
 5000. 2. The method of claim 1, wherein the pH of the aqueous composition is maintained at about 7.4±0.4.
 3. The method of claim 1, wherein said aqueous composition is hypoosmotic, hyperosmotic or iso-osmotic to mammalian body tissues.
 4. The method of claim 1 wherein said aqueous composition forms a gel at mammalian body temperature.
 5. The method of claim 1 wherein the amount of pentoxifylline is between about 0.1% and about 7.0% by weight.
 6. The method of claim 1 wherein the aqueous composition further comprises at least one of carboxymethylcellulose, hydroxyethylcellulose, sodium alginate, xanthan gum, hyaluronic acid or a salt thereof, collagen or polyethyleneglycol.
 7. An aqueous composition for inhibiting internal adhesion formation/reformation following injury to tissues situated in a mammal, said aqueous composition comprising:(1) an effective amount of pentoxifylline; (2) about 60% to about 90% by weight of water, and; (3) about 5% to about 35% by weight of a polyoxyalkylene block copolymer of the formula

    Y((A).sub.n --E--H).sub.x                                  (I)

wherein A is a polyoxyalkylene moiety having an oxygen/carbon atom ratio of less than 0.5, x is at least 1, Y is derived from water or an organic compound containing x reactive hydrogen atoms, E is a polyoxyethylene moiety, n has a value such that the minimum molecular weight of A is between about 500 and about 900, as determined by the hydroxyl number of an intermediate of the general formula

    Y((A).sub.n --H.sub.x                                      (II)

and the average molecular weight of the polyoxyalkylene block copolymer is at least about 5000; wherein said aqueous composition forms a gel at mammalian body temperature.
 8. The composition of claim 7, wherein the pH of the aqueous composition is maintained at about 7.4±0.4.
 9. The composition of claim 7, wherein said aqueous composition is hypoosmotic, hyperosmotic or iso-osmotic to mammalian body tissues.
 10. The composition of claim 7 wherein the amount of pentoxifylline is between about 0.1% and about 7.0% by weight.
 11. The composition of claim 7 wherein the aqueous composition further comprises at least one of carboxymethylcellulose, hydroxyethylcellulose, sodium alginate, xanthan gum, hyaluronic acid or a salt thereof, collagen or polyethyleneglycol. 